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Security Advisory CERT-NL
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Author/Source : CERT-NL (Gert Meijerink) Index : S-94-07
Distribution : World Page : 1
Classification: External Version: Final
Subject : Writable /etc/utmp Vulnerability Date : 01-Apr-94
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CERT-NL received information on a vulnerability that exists on systems
where the file /etc/utmp is writable by any user on the system
The vulnerability is being actively exploited, so take care.
All honours to CERT/CC as provider of the following information
(slightly abridged version):
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The CERT Coordination Center has received information concerning a
vulnerability that exists on systems where the file /etc/utmp is
writable by any user on the system.
This vulnerability is being actively exploited; please review:
CERT-NL Advisory S-94-02 "Ongoing Network Monitoring Attacks".
The problem is known to affect Sun Microsystems, Inc. SunOS 4.1.X operating
systems. Solbourne Computer, Inc. and other Sparc products using SunOS 4.1.X
are also affected. Solaris 1.1.1 and 2.x are not affected by this problem.
Patches can be obtained from local Sun Answer Centers worldwide as well as
through anonymous FTP from:
ftp.nic.surfnet.nl in the surfnet/net-security/cert-nl/patches/sun-fixes
directory.
CERT queried several vendors in addition to Sun. The following vendors
reported that their operating systems, as distributed by the vendor, are
not affected by this problem:
Convex Computer Corporation Digital Equipment Corporation
Data General Corporation Hewlett-Packard Company
IBM Intergraph
Motorola, Inc. NeXT, Inc.
Pyramid Technology Corporation Sequent Computer Systems
Sony Corporation
Currently, we are not aware of /etc/utmp being writable on other systems.
If your operating system is not explicitly mentioned above, and if you
determine that /etc/utmp is writable by someone other than root, we
encourage you to contact your vendor.
If /etc/utmp on your system is writable only by the root account, you need
not be concerned about the vulnerability.
CERT recommends that sites check their /etc/utmp file to be sure it is not
writable by users other than root. If it is generally writable, you should
obtain patches from the system vendor or protect /etc/utmp as described below.
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I. Description
If the file /etc/utmp is writable by users other than root,
programs that trust the information stored in that file can
be subverted.
II. Impact
This vulnerability allows anyone with access to a user account
to gain root access.
III. Solution
The solutions to this vulnerability are to either (a) protect the file,
or (b) patch all the programs that trust it.
A. To protect the file, make /etc/utmp writable only by root:
# chown root /etc/utmp
# chmod 644 /etc/utmp
B. Patches from Sun Microsystems
Program Patch ID Patch File Name
------- --------- ---------------
in.comsat 100272-07 100272-07.tar.Z
dump 100593-03 100593-03.tar.Z
syslogd 100909-02 100909-02.tar.Z
in.talkd 101480-01 101480-01.tar.Z
shutdown 101481-01 101481-01.tar.Z
write 101482-01 101482-01.tar.Z
Program BSD SVR4 MD5 Digital Signature
Checksum Checksum
------- --------- --------- --------------------------------
in.comsat 26553 39 64651 78 912ff4a0cc8d16a10eecbd7be102d45c
dump 52095 242 41650 484 cdba530226e8735fae2bd9bcbfa47dd0
syslogd 61539 108 38239 216 b5f70772384a3e58678c9c1f52d81190
in.talkd 47917 44 32598 88 5c3dfd6f90f739100cfa4aa4c97f01df
shutdown 46562 80 56079 159 bfc257ec795d05646ffa733d1c03855b
write 61148 41 48636 81 f93276529aa9fc25b35679ebf00b2d6f
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CERT-NL is the Computer Emergency Response Team, located in The
Netherlands. CERT-NL is a Full Member of the Forum of Incident Response
and Security Teams (FIRST). The constituency of CERT-NL are the SURFnet
connected institutions.
Past CERT-NL Security Bulletins and other CERT-NL related material can
be found on the anonymous FTP server of SURFnet bv:
"ftp.nic.surfnet.nl" [192.87.46.3], in the directory
"surfnet/net-security/cert-nl/docs/bulletin". This information is also
available using email. Send an email saying "help" to
"mailserv@nic.surfnet.nl".
In case of computer or network security problems please contact CERT-NL
or the CERT of your own constituency. Please be aware of the fact that
we are one (when DST is in effect two) hour(s) ahead of Universal Time
Coordinated (i.e. UTC+0100 (UTC+0200)).
Email: cert-nl@surfnet.nl
Phone: +31 30 310290
Fax: +31 30 340903
Snailmail: SURFnet bv
Attn. CERT-NL
P.O. Box 19035
NL - 3501 DA UTRECHT
The Netherlands
A 7 * 24 hours phone number is available to SURFnet SSC's and FIRST
members on request.
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